Woodkiln molded combustion chamber

ABSTRACT

The molded combustion chamber described herein is an improvement on prior art with a number of significant advantages. A single molded piece replaces many fabricated pieces of board and brick with uniformity of material and lower cost. It can be used by itself as a replacement for a grate in a wood/gas fireplace or as the key element of a metal or masonry fabricated fireplace. It can be molded up to 3″ in thickness, so that the focus can be on insulation and reflection rather than surface durability. The spherical baffle serves as a secondary combustion area, so that all flames are visible and significantly more heat is radiated into the living space. This design is more efficient and less costly than most EPA certified wood heaters with a secondary combustion chamber or catalytic converter. This design will also help a gas appliance meet the DOE efficiency goal. The absence of a grate and the insulating quality of the material used enable a very small coal bed to ignite new fuel. This is user friendly and facilitates the loading of a single large (all-nighter) log for a slow burn. The top of the chamber is flat for heating water and food. This design could be used in a large fireplace and would be particularly useful in underdeveloped parts of the world where there is no other means of cooking than a fire.

The present invention relates in general to combustion chambers and more particularly a wood kiln molded combustion chamber.

BACKGROUND OF THE INVENTION

For background reference is made to the following patents.

7,735,482 June 2010 Meeker 126/504 5,391,074 February 1995 Meeker 431/6 4,681,087 July 1987 Meeker 126/127 4,766,876 August 1988 Henry et al 126/77

An efficient fireplace (EFP) is herein defined as having an insulated combustion chamber and a large glass door to provide a full view of the fire with a high percentage of its heat radiated through the glass. U.S. Pat. No. 4,681,087 illustrates such a construction. (The consumer will buy it for efficiency and cleanliness as well as the feel of radiant heat and view of the fire.)

When the Clean Air Act authorized the EPA to regulate wood burning (1983) no such product existed. The resulting regulation required a wood heater to burn a load of Douglas Fir (2×4s and 4×4s spaced 1.5″ apart) at a very slow rate and defined a fireplace as being very inefficient. Some clever engineering took place resulting in rather complex, airtight, costly and unattractive units such as described in U.S. Pat. No. 4,766,876. The overall result was a decline (much greater than anticipated by the regulators) in new wood burning sales except for exempt units such as outdoor boilers. There are no efficient and low cost wood burning fireplaces. The sales of gas and electric fireplaces have experienced significant growth.

An early version of WoodKiln designed specifically to be a wood heater was the first to be certified to the 1990 standard. However, it was ugly and did not achieve this applicant's goal of an EFP. A later version failed the certification test—not because it was bad for air quality, but because it would not burn slowly enough to be a certified wood heater nor inefficiently enough to be an exempt fireplace.

The EPA is undertaking a 20 year review of its regulation. However, its primary emphasis seems to be to extend the regulation to currently exempt products as opposed to encouraging efficiency and innovation.

In addition to the wood heater test protocol, EPA is relying on an ASTM fireplace test in which it had significant input. Neither of these protocols is realistic for a WoodKiln EFP. They both call for a starting coal bed weight of 20% of the wet weight of the next load. EFP experience says that 5% to 10% is more realistic in terms of user friendliness and getting the new fuel started. The EPA and ASTM protocols both involve spacing the fuel in an unrealistic manner. The net result is to destroy the secondary combustion function of the WoodKiln combustion chamber. Neither protocol includes efficiency in the certification process.

This application involves the concept of a molded combustion chamber for use in an EFP, but which can also be marketed as a replacement for the grate or gas logs in most any fireplace with or without the blessing of the EPA. It also might provide a low cost, clean and efficient cook stove for underdeveloped parts of the world.

SUMMARY OF THE INVENTION

According to the invention, there is a combustion chamber of a single molded shape. The bottom slopes to the rear and the rear is vertical to the bottom. There may be a spherical top that slopes from just above the fuel location in the rear to the full height at the front center. The top front may be constructed and arranged to be used for cooking. An optional gas burner may be installed in the combustion chamber. A metal liner tray may be placed on the bottom for increased durability. The material of the combustion chamber may be a light weight insulating refractory which encourages complete combustion and radiates heat onto the fuel and out the front. The combustion chamber may be a replacement for a fireplace grate. There may be a small coal bed supporting a single large log for a slow burn. The combustion chamber may be incorporated into a low cost prefabricated fireplace insert or a masonry fireplace. Numerous other features, objects and advantages will become apparent from the following detailed description when read in connection with the accompanying drawing in which:

FIG. 1 shows the general shape of the combustion chamber;

FIG. 2 shows a view of a fireplace with a metal box surrounding the combustion chamber;

FIG. 3 is a diagrammatic representation a cold start for a realistic protocol; and

FIG. 4 is a diagrammatic representation of a slow burn for a realistic protocol.

DETAILED DESCRIPTION

FIG. 1 shows the general shape of the molded combustion chamber. The walls are formed in a single operation using insulating refractory material. Their thickness depends on the nature of the material, the molding process, the compromise between good insulation, durability and cost. The insulating quality has more to do with permitting any area to get hot and support combustion in the vicinity as opposed to insulating the chamber from its environment. Currently available materials and molding techniques favor a vacuum-forming process as opposed to a double wall form with material poured into it. About 100 units per 8 hour shift can be produced with a single form. The weight of the finished combustion chamber is between 15 and 45 pounds depending on the wall thickness and density. As a replacement for a fireplace grate, there is no installation involved so that it could be easily marketed. For a gas fireplace the wall thickness might only be 1″, and the whole unit could weigh about 15 pounds. If more durability is needed, a liner tray 1 can be provided. Its purpose is to protect the softer insulating refractory material from abrasion. It will probably be a heavy metal mesh to avoid warping. This is lower in cost than bricks and easier to ship. It will also reduce the overall size and cost of the molded piece.

The bottom 2 is sloped to the rear to prevent logs and coals from rolling out the front without the need for a grate. The rear 3 is sloped to maximize radiant heat out the front. The top 4 is sloped in a spherical fashion to the top front to provide a long hot path for complete combustion in full view, eliminate the need for a secondary combustion chamber or a catalytic converter and maximize radiant heat out the front. The front of the top 5 is flat with a recess focusing the hot gas out the middle so that it can be used for cooking. An optional gas burner 6 similar to U.S. Pat. No. 5,391,074 can be added for starting a wood fire or as a source of heat without burning wood.

FIG. 2 shows an efficient fireplace (or insert) with a metal box 1 surrounding the molded combustion chamber. It has a removable front assembly for servicing purposes. A combustion control 2 as envisioned in U.S. Pat. No. 7,735,482 controls the air supply and the flue draft in such a way that no manual adjustment is required during normal operation. Since most of the combustion process takes place in the chamber below, the primary purpose of the top 3 is heat extraction. Thus the EFP can serve as a relatively low cost cook stove. A vertically operated non-air tight glass door 4 as envisioned in U.S. Pat. No. 4,681,087 seals off the front and permits adjustment of the fuel with a minimum of smoke in the room. It should also be capable of leaning forward for easy cleaning of the glass when necessary.

FIG. 3 shows a cold start for a realistic test protocol. Small rounds are pictured because they are easier to draw. The actual testing might involve one 6″ log measured for moisture and weight and then split into three pieces. The smaller log pieces 1 are placed to the rear. Pieces of wax log lighter 2 are ignited and placed between them. When the lighter and the wood nearby are fully ignited, the third piece 3 is placed diagonally on top so that it does not rest directly on the lighter. This could also be done with two pieces of Douglas Fir 4×4 with one being split for kindling. The molded combustion chamber described herein basically encourages ignition. It does not need an expensive assembled crib as is used in the ASTM fireplace protocol favored by the EPA. There are neither cold, hard refractory walls nor a metal grate.

FIG. 4 shows a slow burn for a realistic test protocol. The coal bed size is normally much smaller (5% to 10% of the wet weight of the next load) than other test protocols used by the EPA (20%) because the molded combustion chamber does not need a large coal bed to ignite the new fuel. A larger coal bed would still be producing significant heat and be uncomfortable for the operator. Typically, there are no flames left when it is time to reload. The coals and ashes are first swept to the sides and then the live coals 1 are mounded in the middle rear. If there is a significant amount of ash remaining on the sides, it is shoveled out. A single large log 2 is placed as far to the rear as possible. For an all-night burn, the diameter could be 10″, and it is recommended that this log be warmed in front of the fireplace before loading. For economical testing it should be 7″ or 8″. Three Douglas Fir 4×4s can be used to simulate a large log. Combustion air 3 comes in the bottom and flames 4 usually start in the middle rear and proceed around the outer surface of the fuel. It is desirable to have glass doors 5 on a fireplace to minimize excessive room air being drawn up the chimney. There is no need to finely split the wood supply because, by the time the core is ready to burn, the kiln effect of the chamber has dried it out. Experience has shown that large rounds properly stored for nine months work well.

There has been described a novel wood kiln molded combustion chamber. It is evident that those skilled in the art may now make numerous uses and modifications of and departures from the specific embodiment described herein without departing from the inventive concept. Consequently, the invention is to be construed as embracing each and every novel feature and novel combination of features present in or possessed by the apparatus and techniques herein disclosed and limited solely by the spirit and scope of the appended claims. 

1-10. (canceled)
 11. A combustion chamber of a single molded shape.
 12. A combustion chamber in accordance with claim 11 having a bottom surface and a rear surface with the bottom surface sloping to the rear surface and the rear surface extending vertically from the bottom surface.
 13. A combustion chamber in accordance with claim 11 having a spherical top that slopes from just above the bottom surface to the full height at the front center of the combustion chamber.
 14. A combustion chamber in accordance with claim 11 and further comprising a gas burner within said combustion chamber.
 15. A combustion chamber in accordance with claim 11 and further comprising a metal liner tray on the bottom surface.
 16. A combustion chamber in accordance with claim 11 made of light weight insulating refractory material.
 17. A combustion chamber in accordance with claim 11 and further comprising a small coal bed on the bottom surface supporting a single large log.
 18. A combustion chamber in accordance with claim 11 having a top formed with a recess focusing the hot gas out the middle so that it can be used for cooking. 